Moisture computer and control system for processing materials having high, indeterminate moisture contents



4 T fi e m MAIN EXTEN FINAL 2 DRYER UNIT DRYER o 43 0. DIFF k a 49 E: ASURING ME July 12, 1966 w. H. CANTER, JR 3,250,642

MOISTURE COMPUTER AND CONTROL SYSTEM FOR PROCESSING MATERIALS HAVING HIGH, INDETERMINATE MOISTURE CONTENTS Original Filed June 27. 1960 52 s PAPER T K Q m n COMPARATOR p I l I STEAM w SU PPLY IO MAIN EXTEN DRYER UNIT MOISTURE CONTENT United States Patent 3,260,642 MOISTURE COMPUTER AND CONTROL SYSTEM FOR PROCESSING MATERIALS HAVING HIGH, INDETERMINATE MOISTURE CONTENTS Walter H. Canter, Jr., Columbus, Ohio, assignor to Industrial Nucleonics Corporation, a corporation of Ohio Continuation of application Ser. No. 38,862, June 27, 1960. This application Dec. 12, 1962, Ser. No. 245,352 11 Claims. (Cl. 162-252) This is a continuation of my copending application Serial No. 38,862, filed June 27, 1960, now abandoned.

This invention relates generally to the measurement and control of moisture content in an industrial process such as a paper making process, and more specifically it relates to a novel method and means for controlling the manufacture of stretchable paper.

Kraft paper is commonly used as a packaging material. This type of paper has a limited energy-absorbing ca pacity. However, an improved stretchable kraft paper has been recently produced in a process whereby a moist paper web is sandwiched between a flexible rubber blanket and a heated drum. Stretchable paper manufactured by this process is commonly referred to as extensible paper or Clupak paper. The moisture content of the paper web entering the extensible unit crucially affects the quality of paper produced. If the moisture content of the web is too high the paper may lose its set before the sheet dries. And, if the web is not sufficiently moistened, deformation of the fibers may not be as complete as it might otherwise be. Up to now, due to the high moisture content of the web, it has been extremely difficult to measure the web accurately enough for purposes of moisture control.

In accordance with the present invention, a pair of nuclear radiation gauges are provided to measure the moisture content of the web. The basis weight of the wet paper at the extensible unit is measured by the first gauge. The paper is dried to a predetermined final moisture content and its combined weight is measured by the second gauge. The measurements are combined to derive a signal proportional to the moisture content of the paper at the extensible unit. The drying rate of the web entering the extensible unit is altered in accordance with this derived signal so that the moisture content of the web is maintained at a substantially constant desired value.

Accordingly, it is a primary object of the present invention to provide a moisture measuring and controlling system for an extensible paper making process.

It is also another object of the present invention to provide a system easily adaptable to paper making processes already in use.

It is a further object of the present invention to provide a control system which in no way interferes with normal process movement.

These and other objects and features of the present invention should become more apparent upon reference to the following description when taken in conjunction with the drawings, in which:

FIG. 1 is a diagrammatic view of an extensible papermaking process controlled in accordance with the present invention; a

FIG. 2 is a partial perspective view of an extensible unit useful in the process of FIG. 1;

FIG. 3 is a graph illustrating the moisture content of the web at certain points in the process of FIG. 1;

FIG. 4 is a diagrammatic view of a modification of the apparatus of FIG. 1;

FIG. 5 is a diagrammatic view of a nuclear radiation gauge comprising a preferred moisture sensor for use in the process of FIG. 1; and,

3,269,642 Patented July 12, 1966 FIG. 6 is a graph illustrating the response of the gauge of FIG. 5 to variations in the weight of the paper web.

with reference now to the drawings and specifically to FIG. 1, a typical extensible papermaking process includes a supply of paper stock 10, a stuff gate 12, a Fourdrinier section 14, a press section 16, and a dryer section 18 which is illustrated in two parts. The main dryer is located at A and the final dryer is located at C. An extensible unit 20 is located at B between the two dryer sections. The paper web 10 traveling in the direction indicated leaves the main dryer, enters the extensible unit 20 to be deformed in a manner described hereinafter and enters the final dryer before being taken up on a reel 22.

Referring now to FIG. 2, extensible unit 20 includes a heated drum 24 over which is stretched a continuous rubber blanket 26 by means of stretch roll 28, a nip roll 30 and a blanket roll 3-2. The paper web 10 is passed between the rubber blanket 26 and the drum 24 and thereby subjected to forces which tend to compress and reorient the individual fibers of the web. A more complete description of the operation of this unit may be found in US. Letters Patent No. 2,721,370, issued October 25, 1955, to S. L. Cluett et al.

The amount of compression imparted to the web 10, and hence its quality, is primarily a function of the moisture of the web entering the extensible unit. The preferred moisture content M of the web entering the extensible unit 20 has a value near thirty-five percent water by weight. In a typical process, the moisture content of the web 10 may vary from twenty-five to fifty percent in accordance with changing process speed, variations in stock input and the inevitable changes in atmospheric humidity. Accordingly, the quality of extensible paper available at the reel has varied from poor to excellent.

Referring to FIG. 3 characteristic 34 illustrates the quasi-linear drying rate of the paper web as a function of its position in the dryer section 18. It may be observed that the preferred moisture content occurs precisely at the location of the extensible unit. However, for reasons stated hereinabove the drying curve may be horizontally displaced to either of the dotted line positions 34a or 34b; whereupon, the moisture of the web at B is respectively greater or less than the preferred value M To correct the foregoing deficiencies in the illustrated embodiment, the present invention provides, in FIG. 1, a first gauge 40 between the extensible unit 20 and the final dryer and a second gauge 42 located between the final dryer and the reel 22. These gauges respectively measure the weight W of the Wet web and the weight D of the dry web. Moreover, gauges 40, 42 may be of the scanning type having profile averaging apparatus associated therewith. A ratio computer 44 computes the percent moisture Since the moisture content of the final dry paper may vary between four and seven percent from process to process, a correction factor 6 is needed in the computation. Since the moisture will be substantially constant for a given process, the compensation may be provided by a potentiometer voltage dividing network. Alternatively, a moisture gauge 45 may be provided for this purpose. Inasmuch as the fiber weight will remain substantially constant from one measuring point to the other in the process, Equation 1 is a valid representation of the moisture content of the web 10 at the extensible unit 20. The output M of the ratio computer 44 is compared at 46 with a signal proportional to M generated by a target setter 48. Any difference between the two inputs to the comparator 46 produces an error signal E Error signal E provides the input to a controller 50 which responds by energizing a two-phase servomotor 52 through a delay device 54. Servomotor 52 actuates a regulator 56 through a suitable gear reduction unit 58. Regulator 56 controls the temperature or pressure of steam flowing from a supply 60 into the main dryer section.

Controller 50 may be designed in accordance with well known principles and may be embodied in any one of a great variety of forms known to persons skilled in the art. Controllers found by applicant to have suitable characteristics for effectively carrying out the operational details incident to the practice of the present invention may be classified into two general types. One type is referred to as a continuous or integrating controller such as is described in a copending application Serial No. 657,434, filed May 6, 1957, by Richard F. Warren, now Patent No. 2,999,406. The other is a reset type controller briefly disclosed herein by way of example, but adequately described in US. Letters Patent 2,895,888, issued July 21, 1959, to D. E. Varner, to which reference may be had.

Alternatively, with reference now to FIG. 4, the first gauge may be located ahead of the extensible unit 20 as at 49'. But the fiber weight per unit area at the reel 22 will be greater than the fiber weight per unit area ahead of the extensible unit 20. This will introduce an error in the moisture computation unless compensated for. The difference in fiber weights is proportional to the differential speed of the web between the measuring points. Therefore, a pair of tachometers 41 and 43 or other suitable speed sensing devices may be respectively located before the extensible unit 20 and after the final dryer to provide signals proportional to the web speed at these points. A difierential speed unit 49 may be used to compute the difference between the signals. The output k of the differential speed unit 49 comprises the input to the moisture computer 44. The moisture computation is continuously modified according to the amount of draw of the extensible unit as reflected in the measured diiferential speed. In this case, Equation 1 becomes ii o) (2) In the operation of the preferred embodiment, controller 50 responds to an increase in detected moisture M by adjusting regulator 56 until the drying rate of the web in the main dryer is sufiicient to provide a web at B having the preferred moisture content M If the web entering the extensible unit should at a later time undergo a reduction in moisture content, controller 50 would reverse servomotor 52 to decrease the drying rate in the main dryer. The magnitude and direction of regulator adjust ment depends on the magnitude and polarity of the error signal E Delay unit 54 suspends control action for a period of time corresponding to the transportation lag of the system. This insures that a second corrective ad justment of dryer temperature is not made until the results of the previous adjustment have been observed at the measuring gauges 40, 42. In this manner the web entering the extensible unit is maintained substantially at the preferred moisture content M Referring now to FIGS. 5 and 6, a nuclear radiation source 62 such as strontium 90 or krypton 85 is mounted adjacent one surface of the web and directs a beam of radiation therethrough toward a radiation detector 64 such as a Geiger-Mueller tube or an ionization chamber. Detector 64 generates an electrical signal proportional to the amount of radiation passing through the web 10. The amount of radiation present at the detector will be a function of the weight of the web 10. Mathematically, the detected intensity I: e-wc where x is mass/unit area of the web and ,u is the mass absorption ooefiicient of the web relative the strength of radiation employed. A measuring circuit 66 and meter 68 may be connected to the detector to indicate the weight. Graphically, the response is illustrated in FIG. 6 by the exponential characteristic 70. Since both the gauges 40 and 42 may be considered identical in response, or calibrated to so obtain, a response R is observed at 40 corresponding to the wet weight W while a larger response R is observed at 42 corresponding to the dry weight D. Although the characteristic 70 is exponential in nature, in the interval of weights normally encountered in the process, the curve may be assumed to be linear.

Although the present invention has been described in accordance with a specific preferred embodiment, the foregoing disclosure should be regarded merely as an example, as numerous additions, substitutions and modifications of the illustrated apparatus may be made without departing from the original spirit and scope of the invention or sacrificing any of its attendant advantages.

I claim:

1. In combination with apparatus for manufacturing stretchable paper from a traveling web varying between 25 and 50 percent moisture by weight including at least an initial dryer section and a final dryer section for removing a predetermined amount of moisture from said traveling web, and an extensible unit located between said dryer sections for shrinking said web, means for measuring the moisture of said web at said extensible unit, means for generating a first signal proportional to said moisture measurement, means for generating a second signal indicative of a preferred value for said moisture, and control means for correctively altering the drying rate of said web entering said extensible unit in accordance with any difference between said two signals.

2. In combination with apparatus for manufacturing stretchable paper from a traveling web varying between 25 and 50 percent moisture by weight including at least an initial dryer section and a final dryer section for removing a predetermined amount of moisture from said traveling web, and an extensible unit ,located between said dryer sections for shrinking said web, means positioned adjacent the output of said extensible unit for measuring the weight per unit area of said web entering said final dryer section, means positioned adjacent the output of said final dryer section for measuring the weight per unit area of said web leaving said final dryer section, means for combining said measurements to provide a first signal proportional to the moisture weight per unit area of said web at said extensible unit, means for generating a second signal indicative of a preferred value for said moisture weight per unit area, and control means for correctively altering the drying rate of said web entering said extensible unit in accordance with any difference between said two signals.

3. In combination with apparatus for manufacturing stretchable paper from a traveling web varying between 25 and 50 percent moisture by weight including an initial drying section and a final drying section for removing moisture from said traveling web, and an extensible unit located between said dryer sections for shrinking said web, means positioned adjacent the output of said extensible unit for measuring the weight per unit area of said Web entering said final dryer section, means positioned adjacent the output of said final dryer section for measuring the weight per unit area of said web leaving said final dryer section, means for combining said measurements to provide a first signal proportional to the moisture weight per unit area at said extensible unit, means for compensating said first signal for variations in moisture of said web leaving said final dryer section, means for generating a second signal indicative of a preferred value for said moisture weight per unit area, and control means for adjusting the temperature of said initial dryer section to maintain the moisture weight per unit area of said Web entering said extensible unit at said preferred value.

4. The subcombination set forth in claim 3 wherein said compensating means comprises a moisture gauge positioned adjacent the output of said final dryer section,

5. In combination with apparatus for manufacturing stretchable paper from a traveling web varying between 25 and 50 perecent moisture by weight including an initial drying section and a final drying section for removing moisture from said traveling web, and an extensible unit located between said dryer sections for shrinking said web, means positioned adjacent the input of said extensible unit for measuring the weight per unit area of said web entering said unit, means positioned adjacent the output of said final dryer section for measuring the weight per unit area of said web leaving said final dryer section, means for combining said measurements to provide a moisture-functional signal, means for measuring the dilferential speed of said web between said weight measuring locations, means for modifying said moisture-functional signal in accordance with said differential speed measurement, means for generating a second signal indicative of a preferred value for said moisture weight per unit area, and control means responsive to said second signal and to said modified moisture-functional signal for adjusting the temperature of said initial dryer section to maintain the moisture weight per unit area of said web entering said extensible unit at said preferred value.

6. The subcombination as set forth in claim 5 wherein said differential speed measuring means comprises a first tachometer positioned adjacent to and responsive to the speed of said web entering said extensible unit, a second tachometer positioned adjacent to and responsive to the speed of said web leaving said final dryer section and computer means connected to said first and said second tachometer.

7. Apparatus as in claim 5 including means for compensating said moisture-functional signal for variations in the moisture content of said web leaving said final dryer section.

8. In an apparatus wherein a traveling material is subjected to a moisture removal operation in passing from a first station where the moisture content of the passing material is high and indeterminate to a second station where the moisture content is relatively low and has a determinate value, gauging means located at each of said stations, each of said gauging means providing a signal indicative of the mass of a local segment of said material passing the respective station, means for generating a signal indicative of said determinate value of moisture content at said second station, and computer means for mathematically combining said moisture content-indicative signal and both of said mass-indicative signals to provide an output signal representing the moisture content of said material passing said first station.

9. Apparatus as in claim 8 wherein said means for generating a signal indicative of said determinate value of moisture content comprises a moisture gauge located at said second station.

10. In an apparatus wherein a traveling material is subjected to a moisture removal operation in passing from a first station where the moisture content of the passing material is high and indeterminate to a second station where the moisture content is relatively low and has a determinate value, a first gauging means located at said first station for generating a signal W representing the mass of a local segment of said material passing said first station, a second gauging means located at said second station for generating a signal D representing the mass of a local segment of said material passing said second station, means for generating a signal 0 representing said determinate value of moisture content at said second station, and means receiving said signals for computing the value of M in accordance with the relationship expressed by D c M 1 W wherein M represents the moisture content of said material passing said first station.

11. In a paper making machine wherein a formed paper sheet is passed through first and second moisture removal means, a first station located between said means where the moisture content of said sheet is high and indeterminate, a second station beyond said second means where the moisture content is relatively low and is indicated by a signal c such as may be provided by a moisture gauge located at said second station, a first gauging means located at said first station for generating a signal W representing the mass of a local segment of said material passing said first station, a second gauging means located at said second station for generating a signal D representing the mass of a local segment of said material passing said second station, means receiving said 0, W and D signals for providing an output computer signal representing the value of M in accordance with the relationship expressed wherein M represents the moisture content of said material passing said first station, and means responsive to said computer output signal for controlling the operation of said first moisture removal means so as to maintain said moisture content M substantially constant at a desired value.

References Cited by the Examiner UNITED STATES PATENTS 2,724,903 11/ 1955 Echrisman 73-73 2,885,763 5/1959 Schreiner 34-123 2,922,475 1/ 1960 Alexander 162-252 2,937,280 5/1960 Gilman 73-73 2,951,007 8/1960 Lippke 162-198 2,966,628 12/1960 Bosch 73-73 3,073,153 1/ 1963 Petitjean 162-263 FOREIGN PATENTS 836,436 4/1952 Germany.

OTHER REFERENCES Petitjean: Non-Destructive Measuring of Drying Profile in Machine Direction, Paper Trade Journal, July 13, 1959, pp. 32-34.

DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK. S. L. BASHORE,

Assistant Examiners. 

8. IN AN APPARATUS WHEREIN A TRAVELING MATERIAL IS SUBJECTED TO A MOISTURE REMOVAL OPERATION IN PASSING FROM A FIRST STATION WHERE THE MOISTURE CONTENT OF THE PASSING MATERIAL IS HIGH AND INDETERMINATE TO A SECOND STATION WHERE THE MOISTURE CONTENT IS RELATIVELY LOW AND HAS A DETERMINATE VALUE, GUAGING MEANS LOCATED AT EACH OF SAID STATIONS, EACH OF SAID GAUGING MEANS PROVIDING A SIGNAL INDICATIVE OF THE MASS OF A LOCAL SEGMENT OF SAID MATERIAL PASSING THE RESPECTIVE STATION, MEANS FOR GENERATING A SIGNAL INDICATIVE OF SAID DETERMINATE VALUE MOISTURE CONTENT AT SAID SECOND STATION, AND COMPUTER MEANS FOR MATHEMATICALLY COMBINING SAID MOISTURE CONTENT-INDICATIVE SIGNAL AND BOTH OF SAID MASS-INDICATIVE SIGNALS TO PROVIDE AN OUTPUT SIGNAL REPRESENTING THE MOISTURE CONTENT OF SAID MATERIAL PASSING SAID FIRST STATION. 